1. Field of the Invention
The present invention relates to a heat sensitive type printer, and more particularly to a cooling fan of the heat sensitive type printer, that is provided for cooling a thermal head and a surface luminous device for optical fixing.
2. Background Arts
The heat sensitive type printer records an image on a heat sensitive recording paper that develops colors when it is heated, by heating the heat sensitive recording paper through a thermal head while moving the heat sensitive recording paper relative to the thermal head. Heat sensitive type color printers for recording full-color images use a heat sensitive color recording paper that has a heat sensitive cyan coloring layer, a heat sensitive magenta coloring layer and a heat sensitive yellow coloring layer which are formed atop another sequentially from a base material. These heat sensitive coloring layers have different heat sensitivities so that these coloring layers may develop colors sequentially from the most sensitive layer, that is, from the topmost layer to the bottommost layer. To stop the already colored coloring layer from being colored by the heat energy applied for coloring the next coloring layer, the already colored coloring layer is optically fixed by electromagnetic rays of a specific wavelength range prior to the heating for the next coloring layer.
There are mainly two types of heat sensitive type color printers: single-head three-pass type and three-head one-pass type. In the single-head three-pass type, the heat sensitive recording paper is passed by a single thermal head three times per one full-color image, to recorded in a three-color frame sequential fashion. In the three-head one-pass type, three thermal head for yellow, magenta and cyan are disposed at appropriate intervals along a transport path of the heat sensitive recording paper, and an optical fixing device for yellow is disposed between the yellow thermal head and the magenta thermal head, whereas an optical fixing device for magenta is disposed between the magenta thermal head and the cyan thermal head.
While the heat sensitive recording paper is being transported in a forward direction, that is, from the side of the thermal head for yellow to the thermal head for cyan, an yellow frame of a full-color image is recorded on the topmost yellow coloring layer, and then the yellow coloring layer is fixed by ultraviolet rays from the yellow optical fixing device. Thereafter while transporting the heat sensitive recording paper still in the forward direction, a magenta frame of the full-color image is recorded on the next magenta coloring layer by applying higher heat energies than those applied for the yellow recording, and the magenta coloring layer is fixed by ultraviolet rays from the magenta optical fixing device. Thereafter, a cyan frame of the full-color image is recorded on the cyan coloring layer by applying higher heat energies than those applied for the magenta recording. In this way, the full-color image is formed on the heat sensitive recording paper as the paper is transported once in the forward direction.
As the optical fixing devices, there are tubular ultraviolet lamps and surface luminous devices. The surface luminous device has a flat light emission surface that is placed to face the heat sensitive recording paper. Luminous intensity of these ultraviolet light sources is affected by the temperature. Specifically, the luminous intensity increases with an increase in temperature of the lamp tube, but above a certain temperature level, the luminous intensity begins to decrease. If the luminous intensity of the optical fixing device varies during the optical fixation, the coloring layer is not uniformly fixed. For this reason, a cooling fan has conventionally been used for keeping the tube temperature in a given range in order to keep the luminous intensity constant.
Concerning the surface luminous device, however, it has been difficult to cool the light emission surface uniformly just by blowing cold air from lateral sides of the light emission surface. Since the light emitting surface of the planer ultraviolet light emitting device extends across the width of the heat sensitive recording paper, that is, in a transverse direction to the paper transporting direction, the method of sending cooling air from the lateral side results unevenness in surface temperature of the light emission surface, and thus unevenness in the optical fixation, particularly in the widthwise direction of the heat sensitive recording paper. Using a lot of cooling fans for uniform cooling results in rising the cost and the size of the heat sensitive type printer. Moreover, the cold air blowing the light emission surface can cool the heat sensitive recording paper and cause unexpected temperature variations of the heat sensitive recording paper, which results improper coloring densities. Also because the cold air can dry the heat sensitive recording paper, and the change in moistness of the heat sensitive recording paper affects the coloring characteristics of the heat sensitive recording paper, it is necessary to prevent the cold air from blowing the heat sensitive recording paper.
In view of the foregoing, an object of the present invention is to provide a heat sensitive type printer that efficiently cools a planer light source without affecting the coloring density of the heat sensitive recording paper.
A heat sensitive type printer according to the present invention comprises a paper transporting device for transporting a heat sensitive recording paper along a paper transport path, the heat sensitive recording paper having at least a coloring layer; at least a thermal head having a heating element array extending in a transverse direction to the paper transport path, the thermal head heating the heat sensitive recording paper through the heating element array as the heat sensitive recording paper is transported along the paper transport path, to record an image line by line on the coloring layer; at least a surface luminous device having a plane light emission surface that faces the paper transport path, for radiating electromagnetic rays toward the heat sensitive recording paper, to fix the coloring layer after having the image recorded thereon; and at least a cooling device for cooling the thermal head and the surface luminous device, the cooling device comprising a cooling air generating device that sends air toward the thermal head and the surface luminous device, and an air guide that guides the cooling air to flow along the light emission surface of the surface luminous device in a lengthwise direction of the paper transport path, to cool the light emission surface.
Since the air that cools the thermal head or the light emission surface of the surface luminous device also cools the other of the thermal head and the light emission surface, both of the thermal head and the light emission surface the single cooling device are cooled with efficiency. Since the air guide guides the cooling air to flow along the light emission surface in the lengthwise direction of the paper transport path, the cooling air is prevented from blowing the heat sensitive recording paper, and thus from influencing the temperature and the moisture of the recording paper.
According to a preferred embodiment, the thermal head and the surface luminous device are disposed adjacent to each other, and the cooling air generating device is disposed above the thermal head and the surface luminous device, and causes the cooling air to flow between the thermal head and the surface luminous device. The air guide is a light permeable plate having one end secured to the thermal head and extending between the light emission surface and the paper transport path substantially in parallel to the paper transport path, so as to conduct the cooling air along a gap between the light emission surface and the air guide.